Deposition rate determination



Aug. 1, 1961 A. DRAVNIEKS DEPOSITION RATE DETERMINATION 2 Sheets-Sheet 1 Filed Oct. 15, 1957 er R N a 0 @WW@ 6 3 OME w M 0 EM 1 R n w 3) u E 3 m R E .1 I 0 3 H 3 4 N 2 m 3 m 5 4 2:? m. /k i \H M E A \AJ 18:42:22 W Y W. Ow Q n 2 P W a 5 M 7J 0 a 2 Y 0 HI //0/I M DI |l l N 2 U 32)) m p 5 S N 6 0 3 5 W c 2 2 4 3 2 3 4 4 ATTORNEY Aug. 1, 1961 A. DRAVNIEKS DEPOSITION RATE DETERMINATION 2 Sheets-Sheet 2 Filed Oct. 15, 1957 N Ql INVENTOR.

Andrew Dmmieks 5.x 0.3mm

ATTORNEY United States Patent 2,994,821 DEPOSITION RATE DETERMINATION Andrew Dravnieks, Park Forest, 11]., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Filed Oct. 15, 1957, Ser. No. 690,397 13 Claims. (Cl. 324-65) This invention relates to a system for making determinations of deposition or coating rates on metal surfaces such as coking in refinery units and in internal combustion engines.

In refining processes, materials frequently are heated under conditions where coke sludge, scale, or varnish may be deposited. Deposition on hot metal surfaces impairs heat transfer. Accordingly, under such conditions, it is advantageous to have a rapid laboratory test to indicate any tendency of a given fluid to form deposits on hot surfaces. When, for instance, coking rates have been determined, material showing strong coking tendencies can be routed through other units where coke formation might be less likely or it may be diluted with material which has less tendency to coke.

Reduced crudes and related streams vary considerably in coking tendencies and additives can be used to control coking rates. The quantity and etficiency of such additives should be determined beforehand and many systems have heretofore been proposed for evaluating the coking tendencies of various liquids and fluids, such as carbon residue tests, but no convenient system has been available for routine coking rate evaluations under controlled heat transfer conditions.

It is, therefore, a primary object of this invention to provide an apparatus which permits routine evaluation of coating tendencies of fluids, particularly where small samples are available. Another object of the invention is to provide an apparatus adapted for use in research investigations wherein fractionation of coking stocks is likely to yield only small fractions for study. An additional object of the invention is to provide a system for investigating the critical factors in coking so as to examine possible means of coking control. A more specific object of the invention is to provide a method and means for measuring coking rates of a multiplicity of samples under controlled conditions. These and other objects of the invention will become apparent as the description thereof proceeds.

Briefly, according to my invention, I provide an apparatus and a technique wherein a specimen is electrically heated by passing A.C. or D.C. currentthrough it, and the electrical resistance of the specimen is measured. A timer mechanism may be provided to make sequential measurements on the specimen whereby the resistance characteristics are measured and recorded automatically as the coating of the specimen proceeds. As the coating is deposited, heat dissipation from the specimen to the fluid is progressively impeded and the temperature of the specimen progressively increases. This increase is measured in terms of the electrical resistance of the specimen.

The system permits testing of coke deposition rates on actual metals encountered in the particular service. For instance, coke deposition rate on aluminum or on steel surfaces can be investigated. This is important since it has been found that coke deposition may be catalyzed by various surfaces in different ways and is also catalyzed by the corrosion products formed on such metal surfaces, corrosion occurring simultaneously with coking at elevated temperatures.

Further details and advantages of embodiments of my system will be described by reference to the accompanying drawings wherein:

\ FIGURE 1 is a schematic diagram of one system; and

Patented Aug. 1, 1961 FIGURE 2 is a schematic diagram of an A.C. bridge circuit adapted to handle several specimens simultaneously.

Referring to the drawings, FIGURE 1 shows schematically the principal components of the coking recorder. It employs A.C. for heating current of this specimen and D.C. for measuring the resistance of the specimen.

A single test uses 300 ml. of oil in a beaker 10 and a specimen strip 11, for example cut from either 0.002 inch or 0.003 inch shim stock to a uniform width of 0.09 inch or 0.13 inch and a length of about 1.5 inches which is clamped between screw clamps 12. Other formed metal specimens 11, such as wires, tubes and ribbons, having uniform metal cross-section may be used. Heavy leads 13 and 14 serve as clamp holders.

Four leads can be used, two each clamping the test specimen 11 on each end. One lead on each end is used to supply the heating current, and another pair to connect to the potential sensing circuit 34. Such a four-lead system avoids influence of the electrical contact resistance (between the specimen and leads) on the measurement of potential drop on the specimen 11.

The oil in the glass beaker 10 is rapidly stirred by stirrer 15 and kept at a selected constant temperature by means of a temperature controller 16, a heater 17, a thermocouple 18, and a fan 19. The strip 11 is heated by 10-15 amperes of A.C. current from the A.C. supply 20 comprising a variable inductance A.C. current adjuster 21 and a high current transformer 22.

The D.C. current supply 23 which is used for the measuring of the electrical resistance consists of a lead storage battery 24, ammeter 25-, iron-hydrogen ballast tube 26 which serves as a current stabilizer, and an adjusting rheostat 27. The rheostat 27 is used to maintain D.C. current to the specimen 11 at a constant level of about 1.0 ampere during the coking test.

The A.C. energy input into the specimen 11 is measured by the watt meter 28. The wattage is adjusted by the current adjuster 21. The condenser 29 prevents D.C. from being short-circuited through the high current side of transformer 22.

During the test both A.C. and D.C. are passed through the specimen strip 11. The D.C. potential drop across the specimen 11 is a measure of the resistance of the specimen and is recorded by means of a recording millivoltmeter 30. The chokes 31 and the condenser 32 keep the A.C. component out from the D.C. recording millivoltmeter 30. The precision potentiometer 33 serves to adjust the input to the millivoltmeter 30. These elements 303 3 comprise the resistance recording circuit 34.

Specimen 11 is placed in a beaker 10 with oil 35. The oil is stirred with stirrer 15 and heated by a heater 17, which is controlled by temperature controller 16 with help of thermocouple 18 inserted in the oil 35. During the test the recorder records the resistance of the specimen 11.

Ammeter 36 measures the current through the beaker heater 17, the current to the beaker heater being adjusted by the variable transformer 37. The temperature of the oil in the beaker 10 may be checked by means of a circuit 38 which may be of the thermistor type.

In order to make records of the specimen resistance in the absence of heating current, the timer 40 disconnects the A.C. current to the specimen 11 at specified intervals or time, for instance, for one minute every fifteen minutes. The strip 11 quickly assumes the oil temperature and the resistance measurement with D.C. current at this temperature permits compensation for any significant corrosion. At the same time the timer 40 disconnects the current to the fan 19 which blows air on the beaker 10 serving to equalize the temperature of the beaker10 during the specimen heating cyclesof the operation. When the specimen heating current is on, the heat generated by the specimen 11 into the oil is removed by the fan 19. This arrangement helps to maintain the oil temperature at constant level through the both cycles of the test.

For simulating pressure and atmosphere conditions, a pressure-tight box 41 which contains beaker 10 with the specimen 11 and the fan 19 is provided. The pressure gauge 42 measures the pressure in the chamber 41. Before the test, the pressure chamber 41 is evacuated to remove air and the vacuum is indicated by the gauge 43. If the pressure chamber 41 is vacuum-tight, it is filled with the desired gas up to the desired pressure. The evacuation of the chamber 41 and filling it with gas is done through line 44.

The chamber 41 permits, for example, running coking experiments in atmospheres of certain gases and also temperatures above the atmospheric boiling points of the oils involved. Many tests do not require pressurized equipment, however. Other instruments, switches, pilot lights, and the like (not shown in the drawings) are not essential to the operation but may be supplied for checking purposes, for making adjustments, and the like in certain parts of the circuit.

For convenient operation of the equipment, it is necessary that the wattage input to the specimen does not change much with the change in the resistance of the specimen. This requires proper selection of resistance of the specimen 11, of condenser 29, of the high current winding of the transformer 22, and of the connecting leads. The resistance of the specimen at room temperature is of the order of 0.06 ohm. The heating current through the specimen may be between 15 and 30 amperes. D.C. current through the specimen is approximately one ampere. Temperatures in the beaker 10 may be between 100 F. and 800 F.

In the operation of the equipment, the constant wattage procedure is a simple one and it helps to establish the relations between various variables, such as pressures and temperatures on one hand, and the coking rate on the other hand.

For the scheduled Wattage procedure the current adjuster 21 is operated mechanically by a slowly turning motor (not shown). This arrangement slowly increases the potential of the high current transformer 22 and thus increases the wattage input in the specimen 11 gradually. In this case, the recorder 30 is an XY recorder with the X axis recording the wattage to the specimen and the Y axis recording the resistance of the specimen 11.

A one-pen recorder is used when runs are made with the constant wattage procedure. Sometimes, to correct for small changes in oil temperature, it is desirable to record also the temperature of the oil. In such cases, a tw-pen XX recorder is used. With the scheduled wattage procedure in which the wattage is increased linearly with time, an XY recorder is more convenient. The A.*C. wattmeter 28 measures the heat input to he strip 11 (the DC). contribution to the heat input can be neglected); usual power inputs are from 100 to 200 watts. To obtain an automatic record, the resistance signal R of potentiometer 33 is fed into the X-axis of a recorder. An auxiliary one-turn potentiometer (not shown) is mounted on the shaft of the X-axis balancing potentiometer of the recorder. An RF type ammeter 28a is tapped at its thermocouple leads and the DC. output of these leads, proportional to the square of the current (I is fed, after being suitably proportioned by the auxiliary potentiometer, into the Y-axis of the recorder, which thus receives the PR signal and records the power input (wattage) to the strip 11. In this way, a continuous indirect record of the temperature of the specimen, and of the heat input into the specimen is obtained; this information permits easy calculation of the heat transfer coefficients.

FIGURE 2. is a schematic circuit of a multiholder design that can handle six specimens 11 simultaneously. .Autotransformer 45 was used for coarse control of the power input. For a fine control, it was necessary to install a second autotransformer 46. This autotransformer 46 feeds a small step-down transformer 47. The output of this transformer 47 is then connected in series with the output of autotransformer 46, the sum of these two A.C. voltages from 45 and 47 being fed into a transformer 48 whose output nominally was rated at 10 volts, 30 amperes. This constitutes the primary power input circuit 49.

A wattmeter 50 measures the power applied to the measuring circuit 51 comprising a number of bridge circuits. The circuit 51 consisted of a manganin resistor 52 used because it maintains a constant resistance fairly independent of temperature. The specimen or strip 11 was connected in series with the resistor 52 to form one pair of the arms of the bridge circuit. The other two resistors 53 and 54 in the bridge comprised two halves of a potentiometer in recorder 55. The recorder amplifier 59 turns the potentiometer 53-54 to a zero balance point (defining bridge resistors 53 and 54) and the recorder 55 indicated where this balance point was. This was then correlated with the resistance of the specimen 11.

The multiholder unit comprises several of these bridges and to minimize duplication of equipment, I provide one wattmeter 50 and only one recorder 55. A mechanical switch 56 permits the wattmeter to be switched to any one of these bridges as desired. A second switch 57 is also necessary for switching to the recorder 55. One side of the bridge is grounded at 58. The switching is done by means of switch 57 which switches the input to the amplifier 59 and also one end of the slide wire on potentiometer 53--54. These two points are switched from bridge to bridge in order to make my measurements.

It is also necessary to measure the resistance of the specimen when no heating current flows through it. In order to accomplish this, a timer 60 reduces the current into the circuit for a small period of time. This permits the recorder 55 to measure the resistance of the specimen 11 with no heating current in it.

In one multiholder unit, six beaker llIlIiS 10 were installed in one cabinet so that six specimens 11, 11a, 11b, 11c, 11d, and He, could be tested simultaneously. When the low current measurements of the specimen resistance were made, current to a strip heater (not shown) immersed in each beaker 10 was turned on to maintain beaker oil temperature. When the high current was again applied to the specimen 11, the current to the strip heater was turned off. In this manner the temperature of the beaker 10 was held constant independently of measuring circuitry and cycle.

In order to operate a unit of this sort, one adjusts the autotransformers 45 and 46 in order to maintain a constant wattage into the unit. It is necessary to maintain a constant wattage into the unit. It is necessary to maintain a constant wattage into the unit because the resistance of the specimen changes as it corrodes. The power into the unit will also change unless it is periodically brought back to its initial value. This is the reason for wattmeter 50 and the very fine control provided by autotransformer 46. The measurements are made regularly and continuously. Switch 57 may be a clock-driven switch which switches from specimen to specimen continuously. Six measurements, one on each specimen, can be made on the order of every two minutes.

Comparing the multiholder circuit of FIGURE 2 with the design of FIGURE 1, the principle of using a heated steel strip 11 immersed in hot oil is the same. In both, record of increase in resistance of strip with buildup of coke and corrosion product deposits is obtained automatically. The arrangements for maintaining the oil at constant temperature are somewhat different. In the earlier design the oil beaker temperature is controlled separately in each beaker. In the multiholder equipment, the several beakers are immersed in a larger temperature-controlled oil bath. In both circuits, a strong A.C. current is used to increase the temperature of the strip specimen 11 well above the temperature of the oil. In FIGURE 1, the resistance of the specimen 11 is measured by means of a DC. component superimposed on the A.C. heating current. In the multiholder design of FIG- URE 2, the resistance record is obtained by the A.C. component alone. Thus in the multiholder design, the DC. power supply 23 and the DC blocking condenser 29 may be eliminated.

Although my invention has been described in terms of several embodiments of the apparatus, which are set forth in considerable detail, it should be understood that these are by way of illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those skilled in the art in View of my disclosure. Accordingly, modifications in the invention are contemplated which may be made without departing from the spirit and scope of the described invention.

What I claim is:

1. An apparatus for making coating rate determinations of a fluid tending to form coatings on a hot surface which includes a test specimen immersed in the fluid under test, means for controlling the temperature of the said fluid during the testing, means for passing an electrical heating current through the said specimen, and electrical measuring circuit means including said specimen for measuring any change in electrical resistance of the specimen due to the formation of coatings thereon.

2. The apparatus of claim 1 which includes a multiplicity of test specimens selectively connectible in such electrical measuring circuit means, a single recorder means in said electrical measuring circuit means, and switch means for selectively connecting each specimen to the recorder means to thereby record the resistance of each of said specimens separately on said single recorder means.

3. The apparatus of claim 1 wherein said means for passing an electrical heating current through said specimen includes means for increasing wattage continuously.

4. The apparatus of claim 1 which includes means for maintaining the temperature of the specimen constant by varying the electrical heating current and means to measure decrease in wattage necessary to maintain the said temperature as a measure of deposition rate.

5. The apparatus of claim 1 wherein said test specimen comprises a formed metal unit of initially constant crosssection.

6. A method for making coating rate determinations of a fluid tending to form coatings on a hot surface which comprises immersing a test specimen in the fluid under test, controlling the temperature of the said fluid during the test, passing a heating current through the test specimen, and measuring any change in electrical resistance of the specimen due to the deposition of coatings formed thereon.

7. The method of claim 6 wherein measurements of changes in electrical resistance are made with the cyclic application of reduced current during said exposure to compensate for resistance change because of the deposition of a coating thereon.

8. The method of claim 6 wherein the coating results from coking of a fluid under test.

9. The method of claim 6 wherein the wattage is varied with time.

10. The method of claim 6 wherein the wattage is decreased to maintain a selected temperature of the test specimen.

11. An apparatus for making coating rate determinations of a fluid tending to form coatings on a hot surface which comprises a test specimen immersed in the fluid under test, means for controlling the temperature of said fluid during the test, means for passing an A.C. heating current through the said specimen, and D.C. measuring circuit means including said specimen for measuring any change in electrical resistance of the specimen due to the deposition of coatings formed thereon.

12. Apparatus of claim 11 wherein said A.C. heating current is maintained at substantially constant wattage, and the change in electrical resistance of the specimen is thereby a measure of the deposition of coatings on said specimen.

13. Apparatus of claim 11 wherein said means for passing an A.C. heating current through the specimen includes means for increasing wattage continuously.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Maimoni: Hot Wire Liquid-Level Indicator, The Review of Scientific Instruments, vol. 27, No. 12, December 1956; pp. 1024-1027.

UNITED STATES- PATENT. OFFICE CERTIFICATE OF CORRECTION Patent N0 2 994 82l August 1 1961 Andrew Dravnieks It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. a

Column 3 line 558 for "he" read the";. colunm 4 lines 56 and 57 strike out "It is necessary to maintain a constant wattage into the unitn".

Signed and sealed this 30th day of January 1962,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES- PATENT. OFFICE CERTIFICATE OF CORRECTION Patent Noo 2 994 821 August 1 1961 Andrew Dravnieks It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. a

Column 3 line 58 for "he" read the ;Y column 4L lines 56 and 57 strike out "It is necessary to maintain a constant wattage into the unite".

Signed and sealed this 30th day of January 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

